• Detection, source location, and analysis of volcano infrasound

      McKee, Kathleen F.; Fee, David; Haney, Matthew; Szuberla, Curt; Tape, Carl; West, Michael (2017-12)
      The study of volcano infrasound focuses on low frequency sound from volcanoes, how volcanic processes produce it, and the path it travels from the source to our receivers. In this dissertation we focus on detecting, locating, and analyzing infrasound from a number of different volcanoes using a variety of analysis techniques. These works will help inform future volcano monitoring using infrasound with respect to infrasonic source location, signal characterization, volatile flux estimation, and back-azimuth to source determination. Source location is an important component of the study of volcano infrasound and in its application to volcano monitoring. Semblance is a forward grid search technique and common source location method in infrasound studies as well as seismology. We evaluated the effectiveness of semblance in the presence of significant topographic features for explosions of Sakurajima Volcano, Japan, while taking into account temperature and wind variations. We show that topographic obstacles at Sakurajima cause a semblance source location offset of ~360-420 m to the northeast of the actual source location. In addition, we found despite the consistent offset in source location semblance can still be a useful tool for determining periods of volcanic activity. Infrasonic signal characterization follows signal detection and source location in volcano monitoring in that it informs us of the type of volcanic activity detected. In large volcanic eruptions the lowermost portion of the eruption column is momentum-driven and termed the volcanic jet or gas-thrust zone. This turbulent fluid-flow perturbs the atmosphere and produces a sound similar to that of jet and rocket engines, known as jet noise. We deployed an array of infrasound sensors near an accessible, less hazardous, fumarolic jet at Aso Volcano, Japan as an analogue to large, violent volcanic eruption jets. We recorded volcanic jet noise at 57.6° from vertical, a recording angle not normally feasible in volcanic environments. The fumarolic jet noise was found to have a sustained, low amplitude signal with a spectral peak between 7-10 Hz. From thermal imagery we measure the jet temperature (~260 °C) and estimate the jet diameter (~2.5 m). From the estimated jet diameter, an assumed Strouhal number of 0.19, and the jet noise peak frequency, we estimated the jet velocity to be ~79 - 132 m/s. We used published gas data to then estimate the volatile flux at ~160 - 270 kg/s (14,000 - 23,000 t/d). These estimates are typically difficult to obtain in volcanic environments, but provide valuable information on the eruption. At regional and global length scales we use infrasound arrays to detect signals and determine their source back-azimuths. A ground-coupled airwave (GCA) occurs when an incident acoustic pressure wave encounters the Earth's surface and part of the energy of the wave is transferred to the ground. GCAs are commonly observed from sources such as volcanic eruptions, bolides, meteors, and explosions. They have been observed to have retrograde particle motion. When recorded on collocated seismo-acoustic sensors, the phase between the infrasound and seismic signals is 90°. If the sensors are separated wind noise is usually incoherent and an additional phase is added due to the sensor separation. We utilized the additional phase and the characteristic particle motion to determine a unique back-azimuth solution to an acoustic source. The additional phase will be different depending on the direction from which a wave arrives. Our technique was tested using synthetic seismo-acoustic data from a coupled Earth-atmosphere 3D finite difference code and then applied to two well-constrained datasets: Mount St. Helens, USA, and Mount Pagan, Commonwealth of the Northern Mariana Islands Volcanoes. The results from our method are within ~<1° - 5° of the actual and traditional infrasound array processing determined back-azimuths. Ours is a new method to detect and determine the back-azimuth to infrasonic signals, which will be useful when financial and spatial resources are limited.
    • Regional variation in mandibular morphology in the prehistoric Japanese populations of the Jōmon and Okhotsk

      Arenas, Rogelio A. (2012-08)
      Examination of 11 metric mandibular traits was conducted on data collected from several Jōmon and Okhotsk sites for the purpose of analyzing potential impacts of dietary differences on mandibular morphology for these groups. Based on the dietary history of the populations and their respective regions, Middle Jōmon (5,000 - 3,000 BP) sites would share comparable robusticities across all regions based on social and economic continuity as a stable climate resulted in abundant dietary resources which fostered a growth in population in the Japanese islands of Honshu and Hokkaido. As the climate cooled in the Late/Final Jōmon (4,000 - 2,000 BP), the population of the two islands crashed coinciding with reduced carrying capacity of the environment due to a reduction in available food resources. Late/Final Jōmon were expected to show mandibular reduction in the Honshu interior which had engaged in plant cultivation and emergent agriculture as opposed to populations on the Hokkaido and Honshu coast which engaged in marine subsistence. The success of agriculture resulted in an expansion across Honshu, pushing marine subsistence communities northeastward to Hokkaido where the tradition persisted as the Epi-Jōmon until the arrival of immigrant populations of the Okhotsk (1,000-600 BP). The Epi-Jōmon and Okhotsk would share comparable robuticities based on their shared practice of marine subsistence. The Late/Final Jōmon and Epi-Jōmon/Okhotsk hypothesis were not supported citing the presence of more diversified and complex subsistence practices than was initially anticipated.
    • Tomo ni manabu: task-based language teaching in a high school English class in Japan

      Holland, Yoshie; Siekmann, Sabine; Murakami, Chisato; Martelle, Wendy (2019-08)
      Task-based language teaching is a method that emerged in the field of second language acquisition in the U.S. Task-based language teaching facilitates language learning in context. However, there are few examples of research that investigate the applicability of task-based language teaching in classrooms in Japan where constraints such as big class size, college entrance exams, and designated textbooks that follow the national curriculum guidelines are factors. This study investigates the response of a Japanese teacher and 41 high school students in Japan, the students' language development as well as the suitability of task-based language teaching in classrooms in Japan. It also offers some guidance to make task-based language teaching more easily applicable to classrooms in Japan. This mixed method study involved a series of semi-structured interviews with a high school teacher in Japan, class observations of the task-based language teaching lessons, and a pre-test and post-test with surveys for the students. The study found out that the teacher expressed tensions between his current teaching context at that time and the task-based language teaching lesson plan. However, the teacher finished the lesson with a positive attitude towards task-based language teaching. Also, the students learned the grammar focus from the task-based language teaching lesson even though the lesson was not focused on the grammar as much as the traditional teaching. Overall, task-based language teaching in the teaching context worked well where the students worked in groups since it facilitated learning among students. This study also suggests that the teacher and his students adopted task-based language teaching positively and that the specific approach of task-supported language teaching is likely to be most suitable in this teaching context.